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Locoweed

Common Name(s):

LocoweedMilkvetchPoisonvetchAstragalus

Scientific Name:

Astragalus L.

Scientific Name Synonyms:

ASTRA

Symbol:

symbol goes here

Description:

Life Span: Annual or Perennial

Origin: Native

Season: Cool

Growth Characteristics: An erect to prostrate forb, with stems that are mostly hairy and leafy. Astragalus
species found in Utah fit into three different categories: 1) Those known not to be
harmful to livestock, of which Cicer milkvetch is the only one; 2) Those harmful to
livestock which produce teratogenisis and embryonic death, known as locoweeds; and
3) Those that accumulate selenium and thus cause damage to livestock, called Milkvetches.
Locoweed starts growth in late fall, winter, or early spring. Milkvetches emerge from
late April to June. Reproduces from seed.

Flowers/Inflorescence:Flowers resemble pea flowers, but smaller in size. Colors vary from white to yellow
to blue to purple, and are arranged in a raceme.

Leaves: Odd-pinnate leaves (a leaflet at the terminal end of the leaf), usually pubescent.

Ecological Adaptions:

Members of the Astragalus are commonly found on foothills and plains and in semiarid
desert regions. They belong to the legume family and are capable of fixing nitrogen
in the soil, thus building soil fertility.

Soils: Adapted to many soils, common in clay, sands, and gravel. Some species of locoweed
are found in soils high in selenium.

Uses and Management:

Locoweed causes "loco" poisoning. Signs of poisoning appear after 2 to 3 weeks of
continuous grazing on the plant. Prevent poisoning by avoiding patches of locoweed
or removing sheep from infested areas of locoweed. Range improvement may be needed
where locoweed occurs. Symptoms of poisoning include: crazed action, uncertainty of
footing (high stepping), head held erect with excited appearance or low, blinking
eyes, leaving the herd, abortion of fetus, inability to eat or drink, and paralysis.
Horses that have been poisoned by locoweed have little value as saddle or draft animals.
Beef cattle with prior poisoning may not make economic gains even though they may
appear to recover.

The poison in milkvetches acts quickly. Some deaths occur within one hour, so fast
that cattle show no signs. Usually animals die within 3 or 4 hours after eating the
plant. Acute poisoning is characterized by a general muscular weakness. It paralyzes
leg muscles so the affected animals fall after the slightest excitement, although
they appear fine. The heart beats very rapidly before the animal dies from heart failure.
Chronic intoxication may occur in animals grazing milkvetch species slowly over a
period of several days or weeks. This type of poisoning is characterized by respiratory
problems and varying degrees of posterior paralysis. Milkvetch is less dangerous after
seed dispersal in July or August.